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Monday May 1st 2017

Posts Tagged ‘M42’

Top 10 Night Sky Objects for Astronomy Beginners

Orion Nebula (M42), Image credit: Wolf DammYour first telescope has just arrived and now you can’t wait to try it out. Trust me, I remember this feeling very well. The universe is calling and it want to be discovered by you. There are so many exciting objects to explore. So, what to aim your telescope at?  I created a list of ten celestial objects that are great for beginners who own binoculars or small telescopes. The targets described represent different kinds of objects that exist in the universe. All objects are easy to find, and their size makes them equally suited for refractors, reflectors, catadioptric telescopes or binoculars. With the exception of the last listing, the Dumbbell Nebula (M27), all objects can be observed even with full moon.

Top 10 Objects for Binoculars and Small Telescopes

Top 10 Night Sky Objects for Astronomy Beginners A short version of the Top 10 Night Sky Objects can be download as PDF and printed. It is a one pager and serves as reference for the field. Links to constellation maps are offered for all stars and deep sky objects. I really recommend a planisphere for beginners; it makes it so much easier finding constellations at a certain day. Alternatively, SkyMaps offers a great monthly two- pager that shows all visible constellations and provides useful further information about current stargazing objects.  These maps are also free and can be downloaded as PDF.




MoonThe Moon is an ever fascinating object that can be observed almost throughout the year. Common presumption is that the moon can be seen best at full moon, but this is actually not the case. The best time is when it is a quarter or less. Sun light comes now from the side and moon features cast long shadows which render the telescope view almost plastic. It is most exciting to observe along moon edges and the Terminator, the line where the dark and illuminated areas come together.

The Moon came into existence when a Mars-size planet crashed into the early Earth. Fragments orbited the Earth and coalesced within just several weeks to become the Moon. The dark areas visible today at the moon are called Maria, from Latin “Sea”. They are meteorite craters that flooded with hot lava. Lava layers can be up to 10 km (6.2 miles) thick, higher than Mount Everest. Diameter: 3 476 km (27% of Earth)
Distance to Earth: 384 000 km (199,000 miles)
Mass: 7.350 x 10E19 tons (1.2% of Earth)
Density: 3.341 g/cm3 (61% of Earth)

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Jupiter is the fifth and largest planet in our solar system. It is a gas giant which is primarily composed of hydrogen and helium (very similar to our sun). Jupiter may also have a rocky core of heavier elements.

Jupiter is the largest planet in our solar system. It is a very bright and exciting object to observe. Four moons can be seen even with small telescopes or binoculars. If the conditions are good some cloud bands are visible, and with larger telescopes it might be possible to see some cloud details and the great red spot.

TIP: It is fun to draw the position of the moons and follow them over a period of time.

Click here for more information about the position of planets.

Jupiter is a gas giant with over 100 moons. The four largest are Io, Europe, Ganymede, Callisto. They are also called the Galilean moons. When Galileo saw the movement of the moons he could no longer accept a geocentric model of the universe. Diameter: 142 980 km (11.2 x Earth)
Mass: 1.899 x 10E24 tons (318 x Earth)
Density: 1.32 g/cm3 (24% of Earth)
Distance from Sun: 4.95 AU

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Saturn, Image credit: Wolf DammSaturn is probably the most enigmatic of all planets. Its rings have given awe to many people who saw it the first time. Since Saturn is double as far from the Sun than Jupiter, it receives only a quarter of the light. While it has almost the size of Jupiter, Saturn’s larger distance results in a smaller, fainter view in the eyepiece. We tend trying to compensate by increasing magnification, but this multiplies air layer disturbances as well. Unless seeing conditions are perfect, a good compromise is a magnification between 100 and 150.

With a very small telescope or under not so good seeing conditions, Saturn’s rings might just be seen as “ears”.  In fact, this is what Galileo saw when he first looked at Saturn with his telescope. He concluded that these “ears” must be two close moons on either side of Saturn, but two years later the moons were gone, and again two years later the moons re-appeared. We know today, that the “disappearance” was caused by looking at the ring edge on but it was very confusing for Galileo at that time.

Click here for more information about the position of planets.

Saturn is a gas giant, and has over 62 moons, with Titan and Rhea as the largest ones. Saturn has a very low density, in fact if we could build a bathtub large enough to hold Saturn, it would float on the surface. Diameter: 123 000 km (9.4 x Earth)
Mass: 0.569 x 10E24 tons (95 x Earth)
Density: 0.67 g/cm3 (24% of Earth)
Distance from Sun: 9.54 AU

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Mizar & Alcor

The Big Dipper is probably the best known asterism for stargazers in the Northern hemisphere. Big Dipper consists of seven stars and belongs to the constellation Ursa Major, or Great Bear. It is easy to find and its serves as guidepost to Polaris. Find the brightest two stars at the outer bowl edge, Dubhe and Merak. Take 5 times their distance and you reach Polaris, the Northern Star.

Mizar & Alcor
Mizar & Alcor (click on image for larger scale)

Big Dipper holds some surprises that are revealed at closer observation. Point your telescope at the handle bend and what you see are not one but two stars. The brighter one is Mizar, the dimmer star is Alcor. They are also known as “Horse and Rider”. People with good eyesight can distinguish these two stars with bare eyes. If the seeing conditions are good, choose high magnification and take a closer look at Mizar. You will see that Mizar itself has another close companion star.  The image above shows an actual photo of Mizar A, his close companion Mizar B and Alcor (click at the image to open a larger scale version).

Click here for a star map of Ursa Major.

The Mizar – Alcor system consists of even more stars that are however too faint for small telescopes. Four stars belong to the local Mizar system and the Alcor system consists of two. New research has revealed that both systems are gravitationally linked, making Mizar & Alcor a true 6-star system. Constellation: Ursa Major, UMa
Magnitude (Mizar/Alcor): 2.2 /4.0
Separation: 11.8′
Distance: 83 Light years
Mass (Mizar/Alcor): 7.7 /2 x Sun, Diameter: 4.1 / 1.8 x Sun
Luminosity: (Mizar/Alcor): 63 / 13 x Sun

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In the night sky: late Spring to Fall.

Albireo, HunterAlbireo is the fifth brightest star in the constellation Cygnus (Swan). With naked eye it appears to be single star but a telescope resolves it as double star. Both stars offer a striking color contrast. The brighter star shines in yellow color, the smaller star in blue.

Image credit: Hunter Wilson.

When observing colorful stars, it can be beneficial to do this somewhat out of focus. Since the star disks become larger, colors become more prominent. The reason for this is that a larger number of color receptors in the eyes can collect color information . Play with your focuser and see what works best for you.

Click here for a star map of Cygnus.

At this point it is unknown whether the stars are optical doubles or gravitational linked and orbiting each other.The brighter star itself has a very close companion, too close though to be resolved with a telescope. Constellation: Cygnus, CYG
Magnitude: A 3.2, B 5.8
Separation 35″
Distance 390 / 390 Light years
Mass: 5 / 3.2 x Sun
Diameter: 16 / 2.7 x Sun
Luminosity: 950 / 120 x Sun

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Orion Nebula (M42)

In the night sky: Winter and Spring.

Orion Nebula (M42)The Orion Nebula is part of the constellation Orion. This truly beautiful nebula can be found just below Orion’s belt as a part of Orion’s sword. It is one of the brightest nebulae and is visible to the naked eye.

Because M42 is over an arc minute wide use your lowest magnification to ensure it fits in the field of view. The four stars at its center are called “Trapezium”, they energize and ionize surrounding gasses which leads to this beautiful spectacle.  Due to its brightness the Trapezium stars draw the observers attention, but scanning the area around them, you will see many smaller stars and layers of ionized gas.

Click here for a star map of Orion.

Orion nebula is the closest region of massive star formation to the Earth. It hosts protoplanetary discs and brown dwarfs. New stars and planets are born here right now. The strong radiation emitted by the Trapezium stars is so powerful that young neighbor stars are pushed into the form of an egg. Constellation: Orion, ORI
Magnitude: 4.0
Size: 65’x60′
Distance 1,344 Light Years
Diameter: 24 Light Years
Mass: 2,000 x Sun

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Andromeda Galaxy (M31)

In the night sky: Summer, Fall and Winter.

Andromeda Galaxy (M31)The Andromeda Galaxy belongs to the constellation Andromeda. It is the farthest object that can be seen with bare eyes. It is so large that it will most certainly exceed the field of your telescope view (binoculars have sufficient viewing angle) Nevertheless is a fascinating moment taking a peak at another Galaxy for the first time. The core is very bright and the surrounding areas can be seen nicely.

There are many ways finding the Andromeda Galaxy in the night sky. My favorite is to extend the most pointy part of the Cassiopeia “W”three times.

Click here for star maps of Andromeda and Cassiopeia.

The Andromeda Galaxy is a spiral galaxy has an estimated 1 Trillion stars (Milky Way 200 – 400 Billion). Its center comprises a massive black whole. Andromeda Galaxy will and the Milky Way are moving towards each other. They will merge in about 4.5 Billion years. Constellation: Andromeda, AND
Magnitude: 3.44
Distance 2.54 Million Light Years
Mass: 1- 1.5 x Milky Way Galaxy

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Hercules  Cluster (M13)

In the night sky: Spring, Summer and Fall.

Herkules Globular Cluster, Image credit: ESA, NASAAs it’s name already reveals, the Hercules Global Cluster lies in the constellation Hercules.  The Globular Cluster is almost as old as the known universe and offers beautiful view even for small telescopes.

Image Credit: ESA, NASA

It is a bit more challenging to find Hercules Globular Cluster. First we have to find “The Keystone”, four stars of the constellation Hercules that build a trapezoid. M13 lies on the line between Eta Herculis and Zeta Herculis. These are the two stars in “The Keystone” at the side of Arcturus. Move a little bit towards Eta on the Eta-Zeta line and you have found this beautiful globular cluster. If you have difficulties to find “The Keystone”, two bright stars, Vega and Arcturus help. Draw a line from Vega to Arcturus, “The Keystone” is located about one third the distance from Vega.

Click here for a star map of Hercules.

Despite it’s age, Hercules Globular Cluster has not changed its form much. Pressure of star radiation pushing stars apart and gravity force pulling them together, resulting in an equilibrium. The stable conditions were thought to be beneficial for possible forming of life. In 1974 a radio message was sent to the Hercules Cluster with the large Arecibo radio telescope. The digital message included information about man, earth and the solar system. Constellation: Hercules, HER
Magnitude: 5.8
Distance 25,100 Light Years
Diameter: 168 Light years
Mass: 600,000 times Sun
Age: 14 Billion years

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Double Cluster (NGC 869 & NGC884)

In the night sky: Fall, Winter, Early Spring.

The Double Cluster (NGC 869 & NGC884), Image credit: Wolf DammIn his classic Field Book of the Stars (1929), William Olcott called the Double Cluster: “One of the finest clusters for a small telescope. The field is simply sown with scintillating stars, and the contrasting colors are very beautiful”. Does this not make anyone thrilled to observe this fine object? What we see are in fact two independent open clusters. They are about 800 light years apart but due to their position in the sky, they fit both in the view of a small telescope.

The Double Cluster belongs to the constellation Perseus. It can be easily found with the help of the constellation Cassiopeia. Just follow the inner leg of the shallow half of the “W” (Cassiopeia Gamma – Delta) about two third of the way to the next bright star, and you will find the Double Cluster.

Click here for star maps of Perseus and Cassiopeia.

The Greeks knew about the object as early as 130 BC, but the true nature of it was not discovered not before the telescope was invented.
The radiant of the Perseid meteor shower (Aug 12 & 13) is located in the neighborhood of the Double Cluster (SW).
Constellation: Perseus, PER
Magnitude: 4.2
Distance (NGC 869): 6,800 Light Years
Distance (NGC 884): 7,600 Light Years
Age (NGC 869): 5.6 Million years
Age (NGC 884): 3.2 Million years

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Dumbbell Nebula (M27)

In the night sky: Fall, Winter, Spring

Dumbbell Nebula (M27), photo credit: Wolf DammWith a magnitude of 7.5 , the Dumbbell Nebula is the faintest object in our Top-10 list. It is however the second largest planetary nebula in the northern sky and can be found relatively easily. The Dumbbell Nebula is located in the constellation Vulpecula, Latin for “Little Fox”. Vulpecula is a very small constellation with faint stars, southwest of Albireo in the constellation Cygnus. My preferred way to find M27 is with the help of the constellation Sagitta, the “Arrow”, just south of it. Its stars are brighter so they are easier to make out. They are shaped like an arrow with feathers (or a triangle  with tip). The Dumbbel Nebula, M27 is pretty exactly north of Sagitta’s tip star, Gamma Saggitae.

Click here for star maps of Vulpecula, Cygnus and Sagitta.

M27 is a planetary nebula. This term was coined by early astronomers who thought these nebulae were planets. In fact, they have nothing to do with planets. Planetary nebulae are clouds of material, shed by a star. It glows because it is excited by radiation emitted by a nearby object. Constellation: Vulpecula, VUL
Magnitude: 7.5
Distance 1,360 Light Years
Diameter: 1.44 Light Years
Central star
Dia: 0.055 Sun, Mass: 0.56 Sun
Age: only 9800 years

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Further Material

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Eyepiece Projection

Eyepiece projection is a great way to take detailed shoots of moon and planets. Photographed objects in these images are considerably larger and show more detail than such taken with prime focus shots. Prime focus techniques replace the camera lens with a telescope OTA (no diagonal, no eyepiece), but eyepiece projection adds an eyepiece into the optical path, increasing focal length and magnification considerably. The image below shows the typical eyepiece projection setup.

Greater magnification and increased focal length come however at a price.  Higher focal length (at the same aperture) results in a higher focal ratio number (1/f). The higher the focal ratio number the fainter the image becomes. This demands longer exposure times or higher ISO speeds to achieve a decent image brightness. Furthermore, constantly moving air layers diffract incoming light. That means, with stronger magnification distortion is magnified as well. The same is true for any mount and telescope shake or vibration.

Eyepiece projection imaging with refractor telescope and DLSR camera Typical eyepiece projection setup with refractor telescope an DSLR camera.

How to do it?

The following paragraphs describe equipment that is needed and such which is additionally recommended to make photographer’s life easier. I will share some experiences that I had to learn the hard way; it will help you getting good results sooner.


  • The mount needs to be strong and sturdy. It has to carry all the weight of telescope, camera and all accessories, furthermore it has to stand steady, even with light breezes.
  • Many manufacturers are quite “generous” when listing weight capabilities of mounts and tripods in their data sheets. Unfortunately, this leads often to unsatisfactory imaging experiences.
  • Never max out a mount load. The old astrophotographers’ rule still applies:  actual equipment weight should not exceed half of the mounts specified load capability.
  • Many astrophotographers do not extend the tripod legs for better stability and minimal vibration.
  • Balance the mount very carefully with camera and all accessories attached.
  • Polar align German Equatorial Mounts (GEM) with great care. It helps “keeping the object in the field of view”, even with highest magnification.

Telescope & Accessories

  • Finder scope and main scope axis need to be perfectly aligned. This helps to “find” the object and framing it in the very narrow field of view (FOV).
  • Screwed accessory connections,like tube extensions, are preferred over slide-in joints. Screwed connections offer better stability, less flex and are less receptive to shake and vibrations.
  • Eyepiece projection requires usually significant focuser back travel, particularly with refractors. The required length can exceed the telescope’s focuser travel, which will render the projection out of focus. One or two 2” extension tubes provide the required additional focusing way. My telescope has sufficient travel way but I still use extension tubes because it keeps the, relatively heavy, focuser tube more inserted. This has the advantage that the telescope’s weight distribution is somewhat closer to the center of the mount (less vibrations).
Astrophotography: Typical Eyepiece Projection Assembly with DSLR Astrophotography: Typical Eyepiece Projection Assembly with DSLR T-Adaptor

Note: M42 and T-thread accessories have different threads. While the diameter is the same their thread pitches are different (M42: M42x1mm and T2: M42x0.75mm). Accessories with M42 and T-threads should never be mated.

The Camera

  • Remote control for the camera is strongly suggested. Pressing the shutter release manually will cause shake and vibrations. If your camera does not have remote capability use your longest shutter release delay, minimum is 10 seconds. Some cameras offer only 2 seconds shutter delay. This time is usually too short because many mounts are still shaking 2 seconds after the shutter button has been pressed.
  • Most cameras allow shooting movie clips (avi). Even if the movie mode may provide less pixel resolution, shoot movie clips, particularly for planetary imaging. Movie clips consist of many single frames and software  like RegiStax convert the movie clip into a string of single images, which can be stacked. With a frame per second rate (fps) of typically 10 fps to 30fps, a 10 second clip results in a large number of single frames. This is important because air movement and other distortions will blur many images. The probability of getting a few good ones increases with the number of available images.
  • Stacking good images helps to pronounce object features and texture.
  • If your camera has no movie (avi) feature take at least 30, better 50 (or even more) images to increase the probability hitting  some really good ones with little of no air movement.
  • DSLR cameras use mirrors that flip up during the exposure. If shooting images (not movie clips) use mirror lock if available. Even if the mirror is very light, the fast movement can create enough momentum to cause shake, which again blurs the image.
    Jupiter is the fifth and largest planet in our solar system. It is a gas giant which is primarily composed of hydrogen and helium (very similar to our sun). Jupiter may also have a rocky core of heavier elements.
    Jupiter – Image taken with eyepiece projection technique (telescope: 900/120mm, eyepiece: 20mm)

Object Position

  • Take shots at planets when they are high in the sky rather than low at the horizon. Positions high in the sky minimize air refraction distortion. Light that travels through the atmosphere is scattered by aerosol droplets and absorbed by dust. These effects cause diffraction rings and reduce the image brightness. High in the sky, light’s atmospheric path is much shorter, reducing distortion effects significantly.
  • There are also disadvantages of high object positions. Particularly when shooting with a large refractor, the camera position is very low. Also, a large refractor with extension tubes and camera mounted may hit the tripod legs in this position. Make sure enough space is left when moving the telescope to the desired object.


  • Remote controlling the camera with a computer is strongly suggested, particularly with a large refractor. Looking in upright position at the computer screen is simply much (!) more convenient than crawling on the ground trying to peek in the – very low hanging – camera screen or finder.
  • The image on a much larger computer screen allows more precise focusing.
  • Take your time when focusing. High magnifications combined with moving air layers can make this quite a challenge.


  • Re-check with some test shots that the focus is still optimal.
  • Check the histogram and ensure that neither end (black or white) is clipped. If data is lost (clipped) it is lost for good, and can no longer be used to build the image. Even the best post processing effort can not bring lost information back.
  • Shoot several movie clips. My recommendation is 10 by 10. Ten clips each ten seconds long. Depending on the fps rate this  will provide you 1000 to 3000 single frames, a good base to work with.
  • Some photographers prefer much longer clips to increase the probability of catching better results. With very long clips it is more likely that shake, vibrations and drift errors are introduced as well. CCD chips get hotter and start to introduce additional noise and hot pixels. Besides, long movie clips result in very large files, making processing somewhat cumbersome.

Post Processing

  • Powerful software like RegiStax (freeware) converts the movie clip (avi) into single images. Furthermore, it aligns the images, selects the best ones and stacks them for best detail. It allows improving the resulting image even more with a great set of post processing features.

Question for Power

It is possible to calculate how much more magnification we get with eyepiece projection over a simple prime focus setup. To determine this, we need to know some dimensions: focal length of telescope and eyepiece, and the telescope aperture. Furthermore we have to measure the distance from the eyepiece lens to the camera’s CCD chip.

The dimensions used in the following example are from an actual eyepiece projection setup that was used when I shot the Jupiter image: Orion EON 120ED refractor with 20mm Eyepiece, 2 extension tubes each 2 inch ( about 50mm) and a Canon EOS T1i DSLR camera.

Focal length of telescope (FLtele): 900mm
Focal length of eyepiece (FLep): 20mm
Distance eyepiece to CCD (Depccd): 100mm
Telescope aperture (TA): 120mm

Eyepiece Projection Magnification - Dimensions to calculate magnification

Magnification over prime focus set up (Mopf)
Mopf= (Depccd-FLep)/FLep
Mopf= (100mm-20mm)/20mm = 4
The image is 4 times larger than that of a prime focus setup.

Focal Length overall EP setup (FLoEPs)
FLoEPs = Mopf * FLtele
FLoEPs = 4 x 900mm = 3600mm
This setup has a focal length of whopping 3.6 meters (141 inches)! The number shows that eyepiece projection focusing can really be a challenge and has to be done carefully in minute steps.

Focal ratio overall EP setup (1/f oEPs)
1/f oEPs = FLoEPs / TA = 3600 / 120 = 30
The original telescope focal ratio of 7.5 has now become 30. The image will be much darker than that of a prime focus setup. Higher ISO speeds particularly for planetary images may be necessary.

Is it worth the challenge?

Most definitely: YES. Eyepiece projection astrophotography is for more advanced star shooters. It is easily among the most challenging processes in amateur astrophotography, not because of the setup but because of the effects that have to be considered and factored in. But with the right equipment and some practice it can be mastered – and the results speak for themselves: clearly visible features of the moon landscape, surface coloration and visible ice caps of Mars or detailed cloud bands of Jupiter make eyepiece projection imaging indeed quite rewarding.


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Solar Dynamics Observatory

Solar Dynamics Observatory 2017-05-01T06:13:01Z
Observatory: SDO
Instrument: AIA
Detector: AIA
Measurement: 171

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